**Core Concept**
Gastrinoma is a rare neuroendocrine tumor that secretes excessive amounts of gastrin, leading to peptic ulcer disease. The best provocative test for diagnosing gastrinoma involves stimulating gastrin secretion to assess its effect on the stomach.

**Why the Correct Answer is Right**
The correct provocative test for gastrinoma is the Secretin-Stimulated Gastrin Test. Secretin, a hormone that inhibits gastric acid secretion, is administered intravenously. In normal individuals, secretin decreases gastrin secretion. However, in patients with gastrinoma, secretin paradoxically increases gastrin secretion, causing an exaggerated gastrin response. This test helps differentiate gastrinoma from other causes of peptic ulcer disease.

**Why Each Wrong Option is Incorrect**
* **Option A:** The Heidelberg capsule test measures gastric acid secretion and is not specific for gastrinoma.
* **Option B:** The fasting gastrin test measures basal gastrin levels but may not be sensitive for gastrinoma diagnosis.
* **Option C:** The pentagastrin test stimulates gastrin secretion but is not as specific or sensitive as the secretin-stimulated gastrin test.

**Clinical Pearl / High-Yield Fact**
The secretin-stimulated gastrin test is a useful diagnostic tool for gastrinoma, but it should be interpreted in the context of clinical presentation and other diagnostic tests.

**Correct Answer:** C.